1. Field of the Invention
The present invention relates to the structure of a microstrip antenna, which is for use in a mobile communication device or a GPS (global positioning system) device.
2. Description of the Background Art
FIGS. 3(a) and 3(b) are structural diagrams showing an exemplary conventional microstrip antenna 25. Referring to FIGS. 3(a) and 3(b), the microstrip antenna 25 has a dielectric substrate 21, and a radiation electrode 22 and a ground electrode 23 which are formed on upper and lower surfaces of the dielectric substrate 21 respectively. The radiation electrode 22 is provided in the form of a rectangle, which is smaller in outline than the dielectric substrate 21. A feeder 24 is connected to a feeding point 22a of the radiation electrode 22 by soldering. The feeder 24 downwardly projects from the lower surface of the dielectric substrate 21, through a through hole 21a which is formed in the dielectric substrate 21 from the feeding point 22a of the radiation electrode 22. The ground electrode 23, which is formed to substantially cover the overall lower surface of the dielectric substrate 21, is notched in a portion around the forward end of the feeder 24.
This microstrip antenna 25 is mounted on a printed circuit board 26 so that the ground electrode 23 is in contact with a surface of the printed circuit board 26. At this time, the forward end of the feeder 24 is inserted in a small hole 26a which is formed in the printed circuit board 26, to project from a back surface of the printed circuit board 26. The ground electrode 23 is soldered to a circuit pattern which is provided on the printed board 26, while the forward end of the feeder 24 is soldered to another circuit pattern which is provided on the back surface of the printed circuit board 26.
FIGS. 4(a) and 4(b) are structural diagrams showing another exemplary conventional microstrip antenna 34. This microstrip antenna 34 comprises a dielectric substrate 31 having an opening portion 31a in its center. A radiation electrode 32 is formed on an upper surface of the dielectric substrate 31, to cover the opening portion 31a. A ground electrode 33 is formed on a nearly overall back surface of the dielectric substrate 31, excluding the opening portion 31a. The radiation electrode 32 is partially downwardly bent to define a feeding terminal 32b. This feeding terminal 32b passes through the opening portion 31a of the dielectric substrate 31 from a feeding point 32a of the radiation electrode 32, to project from a surface of the ground electrode 33.
Similarly to the microstrip antenna 25 shown in FIGS. 3(a) and 3(b), the ground electrode 33 of the microstrip antenna 34 is soldered to a circuit pattern which is provided on a surface of a printed circuit board 35, while the forward end of the feeding terminal 32b is inserted into a small hole 35a formed in the printed circuit board 35 and is soldered to another circuit pattern which is formed on a back surface of the printed circuit board 35.
Thus, each of the aforementioned conventional microstrip antennas 25 and 34 requires the feeder 24 or the feeding terminal 32b projecting from the back surface of the printed circuit board 26 or 35, in order to connect the radiation electrode 22 or 32 with the printed circuit board 26 or 35. Therefore, it is necessary to form the small hole 26a or 35a in the printed circuit board 26 or 35, for passing the feeder 24 or the feeding terminal 32b therethrough. Further, two steps are required for soldering the ground electrode 23 or 33 and the feeder 24 or the feeding terminal 32b to the circuit patterns which are provided on the front and back surfaces of the printed circuit board 26 or 35 respectively. Thus, the steps of mounting the microstrip antenna 25 or 34 on the printed circuit board 26 or 35 are disadvantageously complicated.